This application is the national phase under 35 U.S.C. xc2xa7371 of PCT International Application No. PCT/JP00/04201 which has an International filing date of Jun. 27, 2000, which designated the United States of America.
The present invention relates to a first method of preparing a polyfluoroalkyl (meth)acrylate ester, and a second method of preparing a fluorine-containing acrylic copolymer using the ester obtained by the first method.
A (meth)acrylate ester having a perfluoroalkyl group and a fluorine-containing acrylic copolymer obtained through copolymerization of the (meth)acrylate ester and a monomer, which is capable of copolymerizing with the ester, have been used to impart water- and oil-repellency to textile products.
A polyfluoroalkyl (meth)acrylate ester to be used as a raw material in an industrial method of preparing such a fluorine-containing acrylic copolymer has conventionally been prepared by an operation as follows:
A polyfluoroalkyl iodide having a perfluoroalkyl group corresponding to the above ester is reacted with a (meth)acrylic acid metal salt (for example, potassium salt) in a proper solvent (for example, tert-butanol) (for example, in an ester-forming reaction apparatus 60 in FIG. 2) to obtain, as a reaction product, a suspension containing the polyfluoroalkyl (meth)acrylate ester and the metal iodide (for example, potassium iodide) precipitate derived from the (meth)acrylic acid metal salt. Then, the suspension is subjected to a filtration to separate the metal iodide (potassium iodide) as a solid material from a filtrate. The filtrate is thereafter subjected to a distillation to obtain the polyfluoroalkyl (meth)acrylate ester by separating the solvent (tert-butanol), which solvent may be then recycled.
According to the method described above, as shown in FIG. 2, in the step of filtering the metal iodide in a filtering apparatus 70, a product-based suspension is filtered and co-washed with a solvent, and thereby the polyfluoroalkyl (meth)acrylate ester in a filter cake is dissolved and recovered. Then, water is added to the filter cake and the metal iodide is discharged from the filtering apparatus in the form of an aqueous solution, while the filtering apparatus 70 is dried by heating for the following filtering step. The product-based filtrate separated previously is mixed with the solvent used for co-washing and the mixture is transferred to an evaporator 80, where the solvent and the polyfluoroalkyl (meth)acrylate ester are distilled off in order by a distillation operation, thereby to obtain a polyfluoroalkyl (meth)acrylate ester as a desired product, in an ester receiver 90 and to recover the solvent in a solvent tank 100.
According to the method including such a filtering step, since the metal iodide is discharged from the filtering apparatus 70 in a form of aqueous solution thereof by addition of water to the filter cake of the metal iodide, a small amount of water is introduced into the solvent in the following filtering step of the product-based suspension, resulting in incorporation of water along with the solvent into the reaction product. This water is easily miscible with the solvent such as tert-butanol and then accumulated in the solvent after being introduced into the solvent. In the case where a dehydration operation of the solvent is not carried out, water is circulated along with the solvent to the ester-forming reaction step.
However, since water inhibits the reaction of forming the polyfluoroalkyl (meth)acrylate ester from the polyfluoroalkyl iodide and the (meth)acrylic acid metal salt, the existence of water in the solvent is not preferable. Therefore, it was required to carry out a dehydration treatment if the water content in the solvent was increased before introducing the solvent into the ester-forming reaction step.
Accordingly, if the polyfluoroalkyl (meth)acrylate ester can be prepared without introducing water into the reaction system, the yield of the ester-forming reaction can be improved, and furthermore, the operation of dehydrating the solvent can be omitted, thus turning to its advantage in view of equipment cost.
An object of the present invention is to solve the problems described above and to provide a method of preparing a polyfluoroalkyl (meth)acrylate ester, which is to be used as a raw material of a fluorine-containing acrylic copolymer, without introducing water into the reaction system.
The present invention provides, in one aspect, a method of preparing a polyfluoroalkyl (meth)acrylate ester, which comprises the steps of:
(I) reacting a polyfluoroalkyl iodide with a (meth)acrylic acid metal salt to obtain a reaction mixture containing a polyfluoroalkyl (meth)acrylate ester and a metal iodide, as shown by the reaction scheme (Formula 1):
CnF2n+CH2CH2I+CH2xe2x95x90CXCOOMxe2x86x92
CnF2n+CH2CH2OCOCXxe2x95x90CH2+MIxe2x80x83xe2x80x83(Formula 1)
[wherein X represents H or CH3, n represents an integer within a range from 2 to 26, preferably from 8 to 20, and most preferably from 8 to 14, and M represents an alkali metal element]; and
(II) heating the obtained reaction mixture to evaporate the polyfluoroalkyl (meth)acrylate ester, thereby to separate and recover the polyfluoroalkyl (meth)acrylate ester.
The present invention provides, in another aspect, a method of preparing a fluorine-containing acrylic copolymer, which comprises the step (step (III)) of copolymerizing the polyfluoroalkyl (meth)acrylate ester prepared by the method described above with an ethylenically unsaturated compound capable of copolymerizing with the above ester.